The Punnett square is useful in predicting the possible allele combination and their frequencies for a particular cross.
Punnett square:
It is a diagrammatic squares to calculate or predict the all possible combination of alleles in offspring for a particular cross.
For example-
Cross between 
Rr x rr
where, 
R- dominant = Green color 
r - recessive = Yellow color
The Punnett square of the cross,
              r             r
 R        Rr            Rr         
r         rr              rr
So, from the Punnett square, the possible alleles from the cross are Rr and rr.
Therefore, the Punnett square is useful in predicting the possible allele combination and their frequencies for a particular cross.
To know more about Punnett square,
https://brainly.com/question/14053639